Refactored parts needed for Blackoil in autodiff to get rid of UG dependency.

This patch refactors (hopefully) all parts of opm-core that are needed
by the fully implicite black oil solver in opm-autodiff and that inherently
relied on UnstructuredGrid.

We added a new simple grid interface consisting out of free functions
that will allow us to use CpGrid without copying it to an UnstructuredGrid
by the means of the GridAdapter. Using this interface we have add methods that
allow specifying the grid information (global_cell, cartdims, etc.) wherever
possible to prevent introducing grid parameters for the type of the grid.
Unfortunately this was not possible everywhere.
Merge remote-tracking branch 'origin/opm-parser-integrate' into refactor-for-cpgrid-support

 Resolved Conflicts:
	opm/core/props/BlackoilPropertiesFromDeck.cpp
	opm/core/props/rock/RockFromDeck.hpp
	opm/core/props/satfunc/SaturationPropsFromDeck.hpp
	opm/core/props/satfunc/SaturationPropsFromDeck_impl.hpp
Fix doxygen documentation.
Assume begin_cell_centroid to what the name tells us: an iterator over then centroids.

Therfore we do not need to call center() in getCoordinate. This is done in the iterator
class returned from CpGrid.
Added free method to get the sum of the the faces that are attached to every cell.
Added method to access face normals.
Added traits classes for the type of cell and face centroids.
Added documentation for FaceCellTraits
Made trans_tpfa usable with grids apart from UnstructuredGrid.
Fixed unused parameter warning in initBlackoilStateFromDeck.
Added missing namespace qualifiers.
Added support for computePoreVolume for grids apart from UnstructuredGrid.
Added suport for grid apart from UG for BlackoilPropertiesFromDeck
Remove ambiguous functions increment and getCoordinate from unnamed namespace in favor to those from namespace UgGridHelpers
Refactored WellsManager to partial use without UnstructuredGrid.
Added new implementation header to list of header files.
Refactored EclipseWriter to make it possible to support CpGrid.
[bugfix] Fixed error in initialization of cartdims during non-UG constructor.
[bugfix] Fixed imcrementing the cell centroid.

Imcrementation should be done at the end of the loop body as otherwise
the first cell is skipped and we are out of bounds for the last iteration.
This patch move the increment to the correct location.
[bugfix] Take normalized face normals into account when calculating tpfa.

At least for Cpgrid the face normal is normalized which has to be taken into
account in tpfa_htrans_compute.
We therefore multiply the facenormal with the face area in cases (read Cpgrid)
where this needed.